Piston expander



Dec. 11, 1951 c. F. JOHNSTON PISTON EXPANDER Filed Sept. 22, 1948 I 1 l lV l/IIIIWI/Illd7lllllll/l/lllll/l/V/VWZ IN VEN TOR. (bar/e 5 f/ofi/v/an Patented Dec. 11, 1951 UNITED STATES PATENT OFFICE PISTON EXPANDER.

Charles F. Johnston, Oakland, Calif. Application September 22, 1948, Serial N 0. 50,500

4 Claims.

The invention relates to spring devices which may be applied to the interior of a hollow piston, such as used in internal combustion engines, for expanding the skirt of the piston into better fitted relation with the surrounding cylinder wall and to thereby take up for wear occurring on the piston or cylinder wall.

An object of the present invention is to provide a piston expander of the character described which may be quickly and easily inserted in a piston through the open end thereof, without the use of any special or uniquely designed insertion tool, and while the piston is in place in the engine, and without requiring the disconnection or removal of the connecting rod or wrist pin attachment to the piston.

Another object of the invention is to provide an expander of the character described which, when inserted within a piston, will be positively secured therein and is so constructed as to constantly maintain itself within the piston and against falling out of the open end of the piston, which has heretofore been a cause of occasional failure of other expanders and damage to the engine.

A further object of the present invention is to provide an expander of the character above which applies its expansive force to the piston skirt adjacent the opposite longitudinal ends of the skirt so as to thereby insure a uniform expansion of the skirt over its length and to avoid a barrel-shaping of the piston, which 'hasbeen heretofore obtained with certain types of expanders Still another object of the invention is to provide a piston expander of the character above which is so designed and constructed as to remain substantially cooler in operation than other types of expanders heretofore available, and to accomplish its expansion function without appreciable sliding or frictional action on the piston, whereby the effective life of the expander is greatly lengthened and wear on the piston is reduced to nil.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of the preferred form of the invention which is illustrated in the drawing accompanying and forming part of the specification. It is to be understood, however, that variations in the showing made by the said drawing and description Referring to said drawing:

Figure l is a cross-sectional view of a piston showing the expander of the present invention in inserted position.

Figure 2 is a cross-sectional view of the piston and expander taken substantially on the plane of line 22 of Figure 1.

Figure 3 is a cross-sectional view of the piston and expander taken substantially on the plane of line 33 of Figure 2.

Figure 4 is a cross-sectional view taken substantially on the plane of line 44 of Figure 1.

Figure 5 is a perspective view of the expander.

The expander of the present invention is designed for use with and insertion in a conventiona1 type piston 6 having a closed head end 1 and a cylindrical skirt 8 extending therefrom to an open bottom end 9 and which is additionally provided, intermediate its ends, with internally projecting wrist pin bosses II and I2. The piston here illustrated is of the so-called slipper skirt" type, although, as will be understood, the expander may be used with any of the conventional hollow pistons having either slotted or solid skirts.

The expander generally denoted by numeral I3 is in the form of an oval or rectangular-shaped annulus of spring material, such as spring steel, concavo-convex in the plane of its major axis so as to define a pair of transversely spaced arched sides I4 and I6 having adjacent longitudinal extremities tapered to and joined in common end portions l1 and 18 located substantially in the plane of such axis. The span of the side arches l4 and I6, as viewed in Figure 2, is such as to lie within the interior of the piston skirt 8 with the opposite end portions l1 and I8 of the expander engaged with the interior face I9 of the skirt adjacent the head end 2| and open end 9 respectively of the skirt. The rise of the arch of the sides I 4 and I5 is such, as illustrated in Figure 2, that when the expander is inserted within the skirt with the longitudinal axis of the expander midway between the bosses II and 12,

as shown in Figure 1, the crowns 22 and 23 of the two arches will forcibly and resiliently bear against the exterior surfaces of the wrist pin bosses H and 12. While the wrist pin bosses afford convenient supports for the crowns of the arches, as above described, it will be understood that the expander may be used with pistons having other types of internal projections upon which the arches may be supported, and in some instances of construction the wrist pin of the piston may be used to support the arches.

Preferably, the engagement of the longitudinal movement of the arches.

ends of the expander with the piston skirt is effected by feet or offset tab portions 24 and 26 extending from the end portions I1 and 18 in angular relation to the curvature of the side arches, so as to lie substantially in a chordal plane intersecting the longitudinal extremities of the arches. Desirably also, the feet 24 and 26 are curved slightly in transverse section, as viewed in Figure 4, so as to lie snugly against the concave inner face IQ of the piston skirt, and additionally, the feet are preferably indented as shown at 27 and 28 to provide external protuberances 29 and 3| which will imbed within the wall of the skirt, as shown in Figure 4, and thereby assist in locating the expander in place in the piston. Usually, the lower end .of the skirt is formed with a reinforcing rib providing a shoulder 32 which serves as a stop from outward movement of the lower foot 26, thereby also serving to hold in the expander.

As another and important feature of the expander, it will be noted that the upper foot 24 is inturned relative to the side arches so as to face downward in the piston, and the lower foot 26 is turned outwardly with respect to the arch sides in the direction of the open end of the piston. 'By reason of this arrangement of the feet, the presence of vibration and the flexing of the expander tend to cause the expander to creep in the direction of the head end of the piston, and consequently there is a constant urging of the expander away from the open end during conditions of use.

Another feature of the expander causing it to .hold firmly within the piston is the curvature of i the arched sides. With reference to Figure 2, it will be noted that the curvature of each of the .arches from its crown to its inner end I1 is somewhat-greater than the curvature from the crown to the opposite end 18. Because of this arrangeh ment, the expander, when inserted and under compression, will tend to crowd against the wrist pin boss at a point somewhat above itshorizontal center, thereby strongly resisting the outward This greater curvature of the upper portion of the arch produces an almost right angular relation between the end IT and the foot 24, thereby placing .the end portion I? substantially perpendicular to the longitudinal .axis of the piston. This arrangement of the end portion l1 greatly facilitates insertion of the expander, as .the end portion I! serves as a convenient abutment for the end of any handy rod-type tool, such as a screwdriver. To insert the expander, the end of the tool is placed against the end portion I! and the expander is then pressed into the piston with the side arches l4 and is engaged .under the wrist pin bosses .and the expander is thus pressed inwardly into the piston through its open end until the crown of the arch is moved to and slightly past the horizontal center of the wrist pin bosses as illustrated in the accompanying drawing. In most linstallations the inner end .l] .of the expander is moved to the internal ring shoulder at the head end 2| of the skirt. The annular arrangement of the expander affords an open or relieved central portion which clears .the end of the connecting rod secured to the wrist pin. Accordingly, the expander may be inserted as above described in the piston while the connecting rod and wrist pin are secured to thepiston. This feature is of considerable importance where the expander is used in a repair job of a motor and where the piston is notremoved .forfitting with .new rings.

compress the side arches.

In such case, the mechanic need only remove the crank case pan so as to gain access to the open ends of the pistons, and thereafter insert the expanders into the pistons as above described, through the open bottom ends of the engine cylinders.

Another important feature of the expander is that its resilience and expansive force within the piston is readily adjustable after insertion of the expander. This is accomplished after insertion by pressing inwardly into the piston the lower end portion l8 of the expander, so as to further This adjustment may be quickly and conveniently effected by merely tapping the lower end I8 of the expander into the piston, and due to the construction of the expander as above described, the expander will retain its further compressed shape after such adjustment.

As will be understood from the foregoing and .clear from the drawings, the positioning of the opposite longitudinal ends I! and I3 of thespring side arches adjacent to the top and bottom ends of the skirt insures the application of the expansive action at such skirt ends to thereby produce an expansion of the skirt at its top and bottom, where it is most needed, and thus afiord the piston a more complete bearing and better stabilization against the cylinder wall. By way of contrast, certain other types of expanders have applied the expansive force to the skirt midway of its length, which has had .a tendency to produce a barrel-shaped piston. As will also be appreciated, the amount of required expansion of the skirt is usually relatively small, measured in a few thousandths of an inch, while the span and rise of the side arches are very much greater. Accordingly, the expansion flexing of the skirt is accompanied by an almost imperceptible movement of the expander which is taken up, substantially entirely, within the side arches. Thus, there is no significant sliding or frictional action of the ends of the expander against the interior wall of the skirt or of the crown of the arches against the periphery of thebosses. As a result, frictional wear of either the expander or the piston by reason of the resilient flexing action is substantially non-existent. It will also be noted that the area of contact of the expander within the piston is reduced .to the relatively small areas of the feet 24 and 26 and the narrow engagement of the crowns of the arches with the Wrist pin bosses. Thus, the amount of heat transmitted to the expander from the piston is reduced accordingly. On the other hand, the open construction of the expander and its relatively large unattached radiating surfaces insures the ready dissipation .of the heat which is transmitted to the expander. As a result, the expander remains relatively cool in operation and always within a temperature leaving the temper and strength of the expander unaffected.

I claim:

1. A piston expander comprising, a pair of transversely spaced substantially parallel and coterminous spring arches having their adjacent longitudinal extremities joined in common end portions and being adapted for longitudinal insertion into the open end of a piston skirt to locate said end portions adjacent the inner and outer ends of said skirt, each of saidend portions having a foot inclined from the curvature of the arches so as to lie substantially-in a chordal plane intersecting the longitudinal extremities of said arches, said foot at the inner end portion being inturned in the direction of said arches and the foot at the outer of said end portions being out-turned in the direction away from said arches.

2. A piston expander adapted for insertion in the open end of a piston skirt having internally projecting wrist pin bosses comprising, a blank of sheet spring metal formed in an oval-shaped annulus concavo-convex in the plane of the principal axis of said annulus to define a pair of continuously curved arched sides having their longitudinal extremities joined in common end portions having a span adapted for engagement with said skirt adjacent the inner and outer ends thereof, said arched sides having a rise and being transversely spaced to resiliently engage said wrist pin bosses, the curvature of said arched sides being greater adjacent the inner end thereof than the curvature adjacent the outer end thereof with the crowns of the arches disposed inwardly of the center of the sides so as to engage said bosses inwardly of their horizontal central plane, and feet extending from said end potions in angular relation to said sides and located in substantially the chordal plane of the span of said end portions, the foot at the inner end portion being in-turned and projecting in the direction of said arched sides, the foot at the outer of said end portions being outturned to project away from said arched sides.

3. A piston expander adapted for insertion in the open end of a piston skirt having internally projecting wrist pin bosses comprising, a blank of sheet spring metal formed in an oval-shaped annulus concave-convex in the plane of the principal axis of said annulus to define a pair of curved arched sides having their longitudinal extremities joined in common inner and outer end portions having a span adapted for engagement with said skirt adjacent the inner and outer ends thereof, said arched sides having a rise and being transversely spaced to resiliently engage said wrist pin bosses, feet extending from said end portions and located in substantially the chordal plane of the span of said end portions, said inner end portion rising substantially perpendicularly from the foot thereat for presenting a surface for engagement with an inserting tool, and the said outer portion being relieved to permit insertion thereby and between said arched sides of an elongated inserting tool adapted for engagement with said inner end surface.

4. A piston expander adapted for insertion in the open end of a piston skirt having internally projecting wrist pin bosses comprising, a blank of sheet spring metal formed in an oval-shaped annulus concave-convex in the plane of the principal axis of said annulus to define a pair of curved arched sides having their longitudinal extremities joined in common inner and outer end portions having a span adapted for engagement with said skirt adjacent the inner and outer ends thereof, said arched sides having a rise and being transversely spaced to resiliently engage said wrist pin bosses, feet extending from said end portions and located in substantially the chordal plane of the span of said end portions, the foot at the inner end portion being in-turned and projecting in the direction of said arched sides, the inner end portion rising substantially perpendicular from the foot thereat and cooperating therewith to provide a surface for receiving the forward end of an elongated inserting tool, and said outer end portion being relieved to permit insertion thereby and between said arched sides of said inserting tool.

CHARLES F. JOHNSTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,010,518 Johnston Aug. 6, 1935 2,014,645 Burkel Sept. 17, 1935 2,140,133 Johnston Dec. 13, 1938 2,286,858 Knoebel June 16, 1942 2,292,884 Marien Aug. 11, 1942 2,350,619 Johnston June 6, 1944 

